This invention relates to an improved system for connecting the ends of four sided rectangular sheet metal ducts wherein each duct end is provided with a double walled integral transverse flange.
This invention relates to an improved means for connecting the ends of a pair of sheet metal duct sections. The invention particularly involves an assembly of the type including frame members defining double walled integral transverse flanges located at a duct end with adjacent frame members joined to each other by angular corner connectors.
The prior art, particularly Heilman et al U.S. Pat. No. 4,466,641 and Fischer et al U.S. Pat. No. 4,579,375, the disclosures of which are incorporated herein by reference, disclose duct connecting systems using integral transverse flanges . These arrangements include a first portion extending perpendicularly outwardly from the duct wall and a second portion bent rearwardly from the outer end of the first portion thereby forming opposing channels. The side edges of an arm of a corner connector are adapted to be snapped and crimped into place in these channels for secure assembly. To hold the adjacent duct sections together, the adjacent sections are bolted to each other at their four corner connectors, thereby forming an assembled section of duct.
Apparatus to manufacture the Heilman et al. invention is manufactured and sold by The Lockformer Company of Lisle, Ill. and is referred to in the industry as the TDC (xe2x80x9cTransverse Duct Connectorxe2x80x9d) system. Apparatus to manufacture the Fischer et al duct is manufactured and sold by Engel Industries, Inc. of St. Louis, Mo. and is referred to in the industry as the TDF (xe2x80x9cTransverse Duct Flangexe2x80x9d) system. While both systems have provided the industry with a useful duct system, there remains a need in the industry for improvements to the systems as discussed herein.
FIG. 1 illustrates in cross section the roll-formed shape of the end 10 of one duct, and the roll-formed shape of the end 12 of an adjacent duct as disclosed in Heilman et al. The frame includes a first upturned portion 14 extending perpendicularly outwardly from the duct wall 16 and a second portion 18 bent rearwardly into position opposite an end portion of the duct wall. The distance between the rearwardly bent portion 18 and the end portion of the duct wall substantially corresponds to the width of an arm of a corner connector 20. The side edges of each such arm of a corner connector 20 are adapted to engage the respective surfaces of the rearwardly bent second portion 18 and duct wall end portion whereby the corner connector 20 is held in position relative to the frame by a retainer means defined by the rearwardly bent second portion 18.
The preferred embodiment of the Heilman et al invention includes a third outwardly facing return portion 22 at the outward edge of the rearwardly bent second portion 18 thereby forming a bead 24. A first channel 26 is formed between the bead 24 and the outwardly extending upturned portion 14, and a second channel 28 is formed in the duct wall opposite the first channel 26. The side edges of an arm of a corner connector 20 are adapted to be snapped into place in these channels 26, 28 for secure assembly of the corner connectors relative to a frame. It has been found however that the corner connectors will be displaced during manufacture and transport of the duct. Therefore, the duct flanges must be crimped (not shown in FIG. 1) over the adjacent arms of a corner connector to secure the corner connector in place within a duct flange.
Pursuant to Heilman et al, when assembling one duct with another, the respective frames and associated corner connectors 20 are brought together, and a bolt 30 or other suitable fastener is employed for achieving the desired connection. Prior to completion of this connection, a gasket 32 may be located between the respective frame portions for conventional purposes.
In order to strengthen the resultant duct joint formed by the Heilman et al invention, each of the arms of a corner connector 20 is provided with an offset ear which may be used for retaining a stiffener means, comprising a strip of spring steel or the like. Each stiffener means is held at its end beneath the offset ear and at its sides between channels 26 and 28. Furthermore, a clip 34 may also be engaged around the adjacent frame portions to provide a smooth exposed joint and to strengthen the joint.
The Fischer et al duct flange, illustrated at FIG. 2, uses a modification of the Heilman et al invention and discloses a duct connecting system having an outstanding web portion 36 extending at 90 degrees from the duct wall 38, with an outward-formed tracking ridge 40 spaced inwardly thereof and formed outwardly of the surface of the assembled duct wall 38. At the outer extremity of the web 36 is an outer flange 42 having a turned-under rounded edge 44, formed at an angle slightly in excess of 180 degrees and terminating in a spring margin 46 which extends back toward the web 36 and normally stands inwardly away from the outer flange 42. xe2x80x9cButton lockxe2x80x9d lances are said to be provided through the rounded-back edge 44 projecting aft. The spacing between the web 36 and the tracking ridge 40, which corresponds to the spacing from the web 36 of the somewhat bulbous rounded portion of the turned-under edge 44, is fixed to accommodate the side edges of an arm of a corner connector. The depth between the spring margin 46 and the outer surface of the duct wall 38 between the ridge 40 and the web 36, is such that the leg portions of a corner connector will snap into position and are said to be held by the spring margins 46 and the lanced projections, trapped by the tracking ridge 40. However, it has also been found that corner connectors will fall out of the Fischer et al. duct flange without crimping. Accordingly, the duct flange of the Fischer et al. duct, in practice, is crimped to hold a corner connector in place.
As with the Heilman et al invention, the Fischer et al. duct can be readily joined with an adjacent duct end by means of bolts or fasteners. Furthermore, gasket material may also be located between adjacent frames without difficulty to decrease leakage.
In order to increase duct flange strength about the duct joint formed by the Fischer et al invention, optional reinforcing bars may be utilized between the arms of adjacent corner pieces. Each bar may be snapped in position behind the outwardly-formed ridge 40 and the rounded edge 44 of the outer flange 42, and retained by the lanced projections. If desired, an elongated clip can also be positioned around the joint formed by adjacent duct flanges to support the middle portion of the integral flanges. Incorporation of the clip and reinforcing bar with adjacent duct flanges, helps to prevent bellowing and leakage caused by pressure exerted by materials flowing within the duct.
After issuance of the Heilman et al and Fischer et al patents, the corner connector was manually inserted into the duct flange and then manually crimped with a hammer or the like. This was, among other things, time consuming, hard on the worker and expensive to the sheet metal contractor. These problems were solved by the Cornermatic(copyright) machine sold by Iowa Precision Industries, Inc., Cedar Rapids, Iowa, and covered by U.S. Pat. Nos. 5,321,880 and 5,283,944 to Goodhue. These patents disclose an automated method and apparatus, respectively, for placement of corner connectors in transverse duct flanges. The Cornermatic(copyright) apparatus and method automatically insert a connector, such as described in Goodhue U.S. Pat. No. 5,342,100, in a duct flange and secure the connector within the flange by crimping the outer portion of the flange over the adjacent arms of the corner connector. The inventions of the Goodhue patents have been a commercial success in the industry.
A primary object of the invention is to provide a double walled integral transverse duct flange.
A further primary object of the invention is to provide a transverse duct flange which provides increased strength and rigidity across the joint created by adjacent integral transverse duct flanges.
A further primary object of the invention is to provide a transverse duct flange which will allow for the use of thinner gauge sheet metal in the construction of duct while providing the strength of a conventional duct flange using heavier gauge sheet metal.
Another object of the invention is to provide a transverse duct flange having additional strength which will alleviate the problems of bulging and leakage at adjacent duct flange joints.
A further object of the invention is to provide a transverse duct flange having additional strength which will alleviate the need to insert stiffeners or reinforcing bars, in ceratin applications, into the duct flange in order to strengthen the duct flange as is currently implemented with the prior art flanges.
A further object of the invention is to decrease the number of clips that are engaged about the respective connected adjacent flange portions to prevent leakage.
A further object of the invention is to provide a more cost efficient means of manufacturing and connecting sheet metal duct than the prior art.
The purposes of this invention are accomplished by providing for frame members defining double walled integral transverse flanges located at a duct end with adjacent frame members joined to each other by angular corner connectors. The invention comprises a duct having a transverse double walled flange. The double walled flange comprises an upturned portion extending perpendicularly outwardly from the duct wall, and a second portion bent rearwardly. The outward edge of the rearwardly bent portion is turned-under and rounded back inwardly toward the inside surface of the upturned portion forming a third return portion. This return portion is extended to the inside surface of the upturned portion and thereafter extended along the inside surface of the upturned portion forming a fourth inner wall portion extending perpendicularly inwardly toward the duct wall from the return portion. This inner wall portion terminates at a L-shaped portion.
In the alternative, the return portion may be turned-over and extended to the outside surface of the upturned portion and thereafter extended along the outside surface of the first portion forming an outside wall portion terminating at a L-shaped portion.
The inwardly and outwardly turned return portions disclosed above may form a bead similar to the bead disclosed in the Heilman et al patent thereby defining a first channel formed between the bead and the down-turned portion. A second channel may be formed in the duct wall opposite the first channel. The channel can be formed by creating a depression in the outside of the duct wall, as disclosed in Heilman et al, or by forming an outwardly facing ridge along the surface of the duct wall, as disclosed in Fischer et al. The side edges of an arm of a corner connector are adapted to be positioned into place in these channels, and thereafter the duct flange is crimped over the corner connector to secure it in place.
An additional aspect of the invention is that a second return portion can be formed at the outward end of the L-shaped portion and thereafter extended back over the flange as described above to produce a duct flange having a triple walled flange.
Assembling sections of sheet metal duct having a double walled flange arrangement of the type described by the present invention results in a stronger transverse duct joint. The stronger duct joint allows a contractor to use lighter gauge sheet metal, and ultimately less metal, than he would use if a duct connecting system utilizing the conventional single walled duct flange is implemented. Moreover, the increased transverse duct joint strength recognized when using the present invention potentially alleviates the need for employing stiffeners or reinforcing bars when assembling sections of duct. As a consequence of using lighter gauge sheet metal and removing the need for stiffeners or reinforcing bars, the present invention provides a more cost efficient means of connecting sheet metal duct than previously known.